I've got a Bushmaster upper 14.5" with a Oly lower and tele stock. I replaced the tele stock with a complete A2 butt assem including the A2 buffer and spring. I now have a fail to eject properly issue. Out of 80 rounds about 10 or 12 stuck in the top of the receiver with a second live round under it that was headed for the chamber. This did not happen with the tele stock, buffer, and spring. What to you guys think of me putting spacer in the A2 buffer tube to make the internal length equal to the tele buffer tube and then using the tele buffer and spring in it? BTW the A2 buffer works fine with my A2 20" upper. Do I need to use the tele buffer with the 14.5" and the A2 with the 20"? Am I barking up the wrong tree and the problem is likely elsewhere? Thanks for any help.

HD,
Short tube, short spring, short buffer
Long tube, long spring, long buffer
It's like Coca-Cola, don't mess with the formula.
Problem is likely elsewhere given that the buttstock is installed, and fits, properly.

I would guess that it is either a weak ejector spring, dirty ejector that needs to be cleaned, or possibly a weak extractor spring or worn extractor. It is possible that with the longer extension, it changed the cyclic rate just enough that it cause the marginal operation of the ejector or extractor to become evident.
Try cleaning the ejector first. To do this, first remove the bolt and put a drop of CLP on the bolt face near the ejector. Take a fired case, hook the rim under the extractor and pivot the case head so that the ejector is pushed into its recess. Do this a number of times and the CLP should loosen up any crud that is in the ejector recess, allowing the ejector to move freely. I found this process cured some stove pipe issues I was having with one of my uppers.